324 PHYSICAL GEOGRAPHY. 



No feature in the physical geography of a country is of greater impor- 

 tance in a consideration of its water-power than the number, size, and 

 distribution of its lakes and ponds, and the adaptation of its surface for 

 the construction of artificial reservoirs, and for increasing the capacity 

 of those which have been naturally formed. The importance of this 

 appears when it is remembered that water-power is suitable for extensive 

 manufacturing, where large amounts of capital are invested, only in pro- 

 portion as it is constant and reliable at all seasons of the year. It may be 

 employed for local convenience and by small establishments, even though 

 it be variable at different seasons, and its use wholly suspended during 

 the driest portion of the year ; but it is only when a constant supply of 

 water-power can be depended upon, that it is capable of being advan- 

 tageously employed by large manufacturing corporations, — the greater 

 cheapness of water-power, as compared with steam-power, being more 

 than counter-balanced if business must be interrupted and capital lie 

 idle because of the failure of streams. By lakes, ponds, and artificial 

 reservoirs, the surplus of heavy rains and of snow melting is stored up 

 in the season of excess against the season of dearth. Our natural reser- 

 voirs are of a capacity, too, which man would not presume to imitate by 

 artificial constructions, being also provided almost free of cost, and capa- 

 ble of being put to actual use with insignificant outlay. 



In our climate the need of a reserved water supply is likely to be 

 experienced at two seasons of drouth, — in midsummer, and, to a less 

 degree, in midwinter. Although the amount of rainfall for the different 

 quarters of the year is nearly equal, the increased heat of summer and 

 consequent evaporation, together with the fact that our summer rainfall 

 is to a considerable extent from showers, and subject to greater variable- 

 ness than that of any other season, usually cause our streams to reach 

 their lowest point at some time during the last part of summer, — the period 

 of drouth being in some years protracted, in others scarcely noticeable or 

 wholly wanting. In winter, on the other hand, precipitation takes place 

 largely in the form of snow. The ground itself, in all its upper stratum, 

 is also frozen solid, and yields but small contributions to the streams. 

 The value of reservoirs to provide a supply against the contingency of 

 want at these seasons can scarcely be over-estimated. By these the 

 regulation of the water supply is under the control of the consumer, and 



